SCLOUSE,

Make sure DP is selected on the monitor's on-screen-display (OSD) as the input source.

monitor is set to DP in the (OSD) if I use the DP cable and VGA with that cable, it is a new Dell 43",

PC will not boot up, no dell boot logo, no drive activity when monitor is connected via DP cable in either DP port, but PC will boot when connected to monitor via VGA cable,

PC will boot with no display cable connected and if I plug in monitor via DP cable after booting, all is good